Neoproterozoic S-type granites in the Alxa Block, westernmost North China and tectonic implications: in situ zircon U-Pb-Hf-O isotopic and geochemical constraints
MetadataShow full item record
Reproduced with publisher permission
The Alxa Block in northern China has been traditionally considered as the westernmost part of the Archean North China Craton (NCC). However, recent studies revealed that there are few Archean rocks exposed in the Alxa Block, and the Paleoproterozoic geology of this block is different from that of the western part of the NCC. Thus, the tectonic affinity of the Alxa Block to the NCC and/or other Precambrian blocks needs further investigations. In this study, we carry out integrated analyses of in situ zircon U–Pb age and Hf–O isotopes as well as whole-rock geochemistry and Nd isotopes for the Neoproterozoic Dabusushan and Naimumaodao granites from central Alxa Block. Secondary ion mass spectrometry (SIMS) U–Pb zircon dating results indicate that the Naimumaodao and Dabusushan granite plutons were formed at ca. 930 Ma and ca. 910 Ma, respectively. These granites are peraluminous (A/CNK value >1.0), and contain peraluminous minerals such as muscovite and tourmaline, similar to those of S-type granites. They are characterized by high zircon δ18O values of ca. 8.2 to 12.1 permil, corresponding to a calculated magmatic δ18O value of ca. 10.5 to 14.3 permil, variable zircon εHf(t) values of −6.2 to +3.8 (corresponding to Hf model ages of 2.2 to 1.6 Ga) and whole-rock εNd(t) values of −10.1 to −4.5 (corresponding to Nd model ages of 2.4-1.9 Ga). The petrological and Nd–Hf–O isotopic study indicated that these granites were most probably generated by remelting of dominant (meta)sedimentary rocks in an orogenesis-related compressional environment. There is a clear contrast in the Precambrian geological evolution, including basement rock age data, Precambrian magmatism and detrital zircon age patterns, between the Alxa Block and the NCC. Furthermore, the new in-situ detrital zircon ages on Neoproterozoic (meta)sedimentary rock suggest that Alxa Block is likely related to the Cathaysia Block of South China during the Neoproterozoic, and amalgamated with the NCC since the Early Paleozoic. Thus, our new data suggest that the Alxa Block is most likely a separated Precambrian terrane from the Western Block of the NCC.
Showing items related by title, author, creator and subject.
Phanerozoic amalgamation of the Alxa Block and North China Craton: Evidence from Paleozoic granitoids, U-Pb geochronology and Sr-Nd-Pb-Hf-O isotope geochemistryDan, W.; Li, X.; Wang, Q.; Wang, Xuan-Ce; Wyman, D.; Liu, Y. (2016)The North China Craton (NCC) has been considered to be part of the supercontinent Columbia. The nature of the NCC western boundary, however, remains strongly disputed. A key question in this regard is whether or not the ...
Petrology, geochronology and geochemistry of ca. 780 Ma A-type granites in South China: Petrogenesis and implications for crustal growth during the breakup of the supercontinent RodiniaWang, Q.; Wyman, D.; Li, Zheng-Xiang; Bao, Z.; Zhao, Z.; Wang, Y.; Jian, P.; Yang, Y.; Chen, L. (2010)There are widespread Neoproterozoic (830–740 Ma) calc-alkaline intrusive rocks in the South China Block, which has been considered a part of the Precambrian supercontinent Rodinia. The tectonic setting of these rocks, ...
Paleoproterozoic evolution of the eastern Alxa Block, westernmost North China: Evidence from in situ zircon U–Pb dating and Hf–O isotopesDan, W.; Li, X.; Guo, J.; Liu, Y.; Wang, Xuan-Ce (2012)The Alxa Block is the westernmost part of the North China Craton (NCC). In the past, it has been considered to be part of the Archean NCC. However, formation and evolution of this block remain poorly understood, and this ...